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fonts-and-faces-native-opentype.html
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fonts-and-faces-native-opentype.html
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<title>Font objects and HarfBuzz's native OpenType implementation: HarfBuzz Manual</title>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fonts-and-faces-native-opentype"></a>Font objects and HarfBuzz's native OpenType implementation</h2></div></div></div>
<p>
By default, whenever HarfBuzz creates a font object, it will
configure the font to use a built-in set of font functions that
supports contemporary OpenType font internals. If you want to
work with OpenType or TrueType fonts, you should be able to use
these functions without difficulty.
</p>
<p>
Many of the methods in the font-functions structure deal with
the fundamental properties of glyphs that are required for
shaping text: extents (the maximums and minimums on each axis),
origins (the <code class="literal">(0,0)</code> coordinate point which
glyphs are drawn in reference to), and advances (the amount that
the cursor needs to be moved after drawing each glyph, including
any empty space for the glyph's side bearings).
</p>
<p>
As you can see in the list of functions, there are separate "horizontal"
and "vertical" variants depending on whether the text is set in
the horizontal or vertical direction. For some scripts, fonts
that are designed to support text set horizontally or vertically (for
example, in Japanese) may include metrics for both text
directions. When fonts don't include this information, HarfBuzz
does its best to transform what the font provides.
</p>
<p>
In addition to the direction-specific functions, HarfBuzz
provides some higher-level functions for fetching information
like extents and advances for a glyph. If you call
</p>
<pre class="programlisting">
hb_font_get_glyph_advance_for_direction(font, direction, extents);
</pre>
<p>
then you can provide any <span class="type">hb_direction_t</span> as the
<em class="parameter"><code>direction</code></em> parameter, and HarfBuzz will
use the correct function variant for the text direction. There
are similar higher-level versions of the functions for fetching
extents, origin coordinates, and contour-point
coordinates. There are also addition and subtraction functions
for moving points with respect to the origin.
</p>
<p>
There are also methods for fetching the glyph ID that
corresponds to a Unicode code point (possibly when followed by a
variation-selector code point), fetching the glyph name from the
font, and fetching the glyph ID that corresponds to a glyph name
you already have.
</p>
<p>
HarfBuzz also provides functions for converting between glyph
names and string
variables. <code class="function">hb_font_glyph_to_string(font, glyph, s,
size)</code> retrieves the name for the glyph ID
<em class="parameter"><code>glyph</code></em> from the font object. It generates a
generic name of the form <code class="literal">gidDDD</code> (where DDD is
the glyph index) if there is no name for the glyph in the
font. The <code class="function">hb_font_glyph_from_string(font, s, len,
glyph)</code> takes an input string <em class="parameter"><code>s</code></em>
and looks for a glyph with that name in the font, returning its
glyph ID in the <em class="parameter"><code>glyph</code></em>
output parameter. It automatically parses
<code class="literal">gidDDD</code> and <code class="literal">uniUUUU</code> strings.
</p>
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